This proposal concerns the search for, evaluation of, and commercial production of improved scintillator crystals for positron emission tomography (PET) arrays for medical research and the diagnosis of cancer and Alzheimer's disease. It is intended to complement and augment an existing Public Health Service NCI grant (R01 CA48002: "Search for Ultrafast, Heavy-Atom Scintillators") currently in progress at the Lawrence Berkeley Laboratory and all Phase I activities will be carried out in collaboration with LBL. Phase I goals are (1) use of crystallographic and experimental search strategies to identify the most likely candidate materials, (2) evaluation of techniques for large-scale growth of crystals of promising candidate materials, and (3) acquisition and/or synthesis of crystals and/or polycrystalline samples of the best candidate materials for evaluation by LBL. Phase II aims will be (4) optimization and exhaustive testing of the most promising candidate materials, and (5) the development of commercial processes for the growth of these crystals. The ultimate Phase III objective is the commercial growth and distribution of optimal PET scintillator crystals for PET medical research and diagnosis systems.